Compositions for bis-(fluoromethyl)ether

ABSTRACT

A composition comprising bis(fluoromethyl)ether and less than an equimolar amount of water, a process for the production of the composition comprising contacting formaldehyde with hydrogen fluoride and separating at least some of the by-product water from bis(fluoromethyl)ether, and use of the composition for the production of difluoromethane.

This is a continuation of application Ser. No. 07/898,786, filed on Jun.15, 1992, which was abandoned upon the filing hereof.

This invention relates to bis(fluoromethyl)ether compositions, a processfor the production of the bis(fluoromethyl)ether compositions, and to aprocess for the production of difluoromethane from thebis(fluoromethyl)ether compositions.

In recent years chlorofluorocarbons, which are used on a large scalearound the world, have been perceived as having an adverse effect on theozone layer and/or as contributing to global warming.Chlorofluorocarbons are used, for example, as refrigerants, as foamblowing agents, as cleaning solvents and as propellants for aerosolsprays in which the variety of applications is virtually unlimited.Consequently, much effort is being devoted to finding suitablereplacements for chlorofluorocarbons which will perform satisfactorilyin the many applications in which chlorofluorocarbons are used but whichwill not have the aforementioned environmentally harmful effects. Oneapproach in the search for suitable replacements has centred onfluorocarbons which do not contain chlorine but which may containhydrogen. The hydrofluorocarbon difluoromethane, also known as HFA 32,is of interest as one such replacement, in particular as a replacementin refrigeration, air-conditioning and other applications.

Several methods for the production of difluoromethane are known but manyof these methods involve the use of chlorine-containing startingmaterials and the production of chlorine-containing by-products.Chlorine-free processes are also known and one of these, the reactionbetween formaldehyde and hydrogen fluoride at an elevated temperature inthe presence of a fluorine-containing inorganic acid, a metal fluoride,a metal oxide or a metal chromite, has been described in U.S. Pat. No.3,377,394. The highest yield of difluoromethane reported from thisreaction is 4.2%, the major product being methyl fluoride.

The present invention resides in our finding that certainbis(fluoromethyl)ether compositions are particularly useful as startingmaterials for the production of difluoromethane, and that suchbis(fluoromethyl)ether compositions may be readily produced.

According to a first aspect of the present invention there is provided acomposition comprising bis(fluoromethyl)ether and wherein thecomposition comprises less than an equimolar amount of water relative tobis(fluoromethyl)ether.

We have found that such bis(fluoromethyl)ether compositions may besimply converted to difluoromethane with high yields of difluoromethaneand without the production of any significant amounts of any toxicby-products.

Generally we prefer that the composition comprises as small an amount ofwater as possible, and the molar ratio of bis(fluoromethyl)ether towater in the composition is usually at least 2:1, preferably at least10:1, more preferably at least 20:1 and especially at least 50:1.Optimum yields of difluoromethane are achieved using compositionssubstantially free from water.

Other materials, for example unreacted starting materials from which thebis(fluoromethyl)ether has been produced and other by-products, may bepresent in the composition, but overall the bis(fluoromethyl)ethercomposition may comprise at least 20 mole % bis(fluoromethyl)ether,preferably at least 35 mole % bis(fluoromethyl)ether, more preferably atleast 50 mole %, particularly preferably at least 70 mole %bis(fluoromethyl)ether, and especially at least 90 mole %bis(fluoromethyl)ether.

Processes are known for the production of bis(fluoromethyl)ether,molecular formula FH₂ COCH₂ F, all of which however result incompositions comprising substantial amounts of water and otherby-products. Furthermore, The bis(fluoromethyl)ether compositions of theinvention may be prepared by any one of these known routes, for exampleby reaction of α-polyoxymethylene, (CH₂ O)_(n), with sulphurtetrafluoride as described in The Journal of Inorganic NuclearChemistry-32, (1970), 1748, or by reaction of trioxane with sulphurtetrafluoride as described in The Journal of the American ChemicalSociety 82 (1960) 543 or by reacting paraformaldehyde with hydrogenfluoride in the liquid phase in the absence of a catalyst as describedin The Journal of Organic Chemistry, 28, 492(1963), so long as steps aretaken to ensure that the bis(fluoromethyl)ether compositions which areproduced comprise at least less moles of water thanbis(fluoromethyl)ether, and preferably at least 20 mole %bis(fluoromethyl)ether.

However, many of these routes employ highly toxic and expensive startingmaterials and they are not suitable for the large scale manufacture ofbis(fluoromethyl)ether. Preferably therefore, the bis(fluoromethyl)ethercomposition of the invention is prepared by contacting formaldehyde withhydrogen fluoride in the liquid phase, or in the vapour phase in thepresence of a catalyst such as an activated carbon. The activated carbonmay also be charged with, for example a metal fluoride such as potassiumor caesium fluoride.

According to a second aspect of the invention there is provided aprocess for the production of bis(fluoromethyl)ether which comprisescontacting formaldehyde with hydrogen fluoride and separating at least apart of the by-product water from the bis(fluoromethyl)ether produced.We especially prefer to react formaldehyde with liquid hydrogenfluoride; this reaction may be effected simply by dissolvingformaldehyde in liquid hydrogen fluoride under conditions of temperatureand pressure whereby hydrogen fluoride is in the liquid phase. Thereaction may be conveniently effected at about ambient temperature andpressure although temperatures above or below ambient andsuperatmospheric or subatmospheric pressures may be employed providedthat hydrogen fluoride is in the liquid phase.

The formaldehyde may be provided in any of its known forms, for examplein one of its polymeric forms, paraformaldehyde or trioxane, or in itsmonomeric form which may be provided, for example, from a process streamin which it has been freshly made, for example by oxidation of methanol.Accordingly, whenever used herein, the term "formaldehyde" is to beunderstood as including not only the monomer but also the variouspolymeric forms, which may be provided, for example in the form ofaqueous solutions. In general, a polymeric form of formaldehyde such asparaformaldehyde is preferred where the formaldehyde is dissolved inliquid hydrogen fluoride to form bis(fluoromethyl)ether.

Paraformaldehyde and trioxane dissolve readily in liquid hydrogenfluoride and the production of bis(fluoromethyl) ether may beconveniently carried out by dissolving paraformaldehyde or trioxane inliquid hydrogen fluoride at about room temperature and at aboutatmospheric pressure. The invention will be described hereafter withreference to bis(fluoromethyl)ether which is produced in this wayalthough the invention is not limited thereto.

The molar ratio of formaldehyde to hydrogen fluoride may varyconsiderably, for example in the range about 1:0.5 to 1:50 but ingeneral a stoichiometric excess of hydrogen fluoride is preferred.Typically, the molar ratio of formaldehyde to hydrogen fluoride will bein the range about 1:2 to about 1:10.

Formaldehyde and hydrogen fluoride react together in the liquid phase toproduce bis(fluoromethyl)ether and water according to the equation:

    2CH.sub.2 O+2HF⃡CH.sub.2 F--O--CH.sub.2 F+H.sub.2 O.

The product is therefore a mixture of unreacted hydrogen fluoride andformaldehyde, water and bis(fluoromethyl)ether. We have discovered thatit is essential, for the further treatment of the bis(fluoromethyl)etherin order to produce difluoromethane, to separate at least part of thewater from the bis(fluoromethyl)ether. Thus, by "separation of at leasta part of the water from bis(fluoromethyl)ether", there is meant simplythat these two components of the product mixture are at least partlyseparated from each other without limitation to separation of the othercomponents of the mixture. Thus for example, the water may be separatedfrom all the other components of the mixture including bis(fluoromethyl)ether, or the bis(fluoromethyl)ether may be separated from all the othercomponents of the mixture including water. We generally prefer that thebis(fluoromethyl)ether, and optionally hydrogen fluoride, is separatedfrom the other components of the mixture.

Separation of the bis(fluoromethyl)ether from water may be achieved inany suitable manner, for example by vaporising thebis(fluoromethyl)ether and optionally hydrogen fluoride from the productmixture obtained by reacting formaldehyde with hydrogen fluoride, or bycontacting the product mixture with a solid drying agent. Thus, forexample a stream of an inert gas, for example nitrogen may be spargedthrough the solution of bis(fluoromethyl)ether (and any unreactedformaldehyde and by-product water) in hydrogen fluoride.

The bis(fluoromethyl)ether may be separated from the water as thereaction proceeds, or they may be separated as a subsequent step afterthe reaction has taken place. Thus, for example, thebis(fluoromethyl)ether may be isolated from the formaldehyde andhydrogen fluoride, from which it is produced, water and any otherby-products, before the bis(fluoromethyl)ether is further treated. Thebis(fluoromethyl)ether may be isolated, for example, by adding alkali tothe paraformaldehyde/hydrogen fluoride liquid mixture and heating theresulting alkaline solution, for example up to about 50° C., in order todrive the bis(fluoromethyl)ether off. Alternatively thebis(fluoromethyl)ether may conveniently be isolated by contacting theproduct stream with water at a temperature in the range from about 50°to about 80° C. The bis(fluoromethyl) ether may then be collected in acold trap or passed directly, after drying, to a reaction vessel or zonefor conversion to difluoromethane as described hereinafter.

However, the liquid phase reaction between formaldehyde and hydrogenfluoride is equilibrium limited, there being about a 60% conversion offormaldehyde to bis(fluoromethyl)ether and water at 20° C. using asubstantial excess of hydrogen fluoride to drive the equilibrium towardsthe products. It is desirable therefore that one or both of theproducts, water and bis(fluoromethyl)ether is separated from thereaction mixture as soon as possible after it is formed in order tofurther drive the equilibrium towards the products and force thereaction to completion, thereby achieving higher conversions ofreactants to products. Furthermore, it is believed that the reaction offormaldehyde with liquid hydrogen particularly useful as startingmaterials for the production of difluoromethane.

According to a third aspect of the present invention there is provided aprocess for the production of difluoromethane which comprises feedingbis(fluoromethyl)ether to a reaction zone whereby to producedifluoromethane.

The process of the third aspect of invention may be operated to formdifluoromethane with yields of at least 5%, preferably at least 20%,more preferably at least 50% and especially at least 70%, based upon theamount of bis(fluoromethyl)ether fed to the reaction zone.

Preferably the bis(fluoromethyl)ether compositions of the first aspectof the invention, that is bis(fluoromethyl)ether compositions containingless than an equimolar amount of water, are employed to effect thisthird aspect of the invention and more preferably thebis(fluoromethyl)ether compositions are prepared by the second aspect ofthe invention.

Thus, according to a first preferred embodiment of the invention thereis provided a process for the production of difluoromethane whichcomprises (a) contacting formaldehyde with liquid hydrogen fluoride tofrom a product comprising bis(fluoromethyl)ether and water, (b)separating at least a part of the water from the bis(fluoromethyl)etherand (c) feeding the bis(fluoromethyl)ether to a reaction zone whereby toproduce difluoromethane.

According to a second preferred embodiment of the invention there isprovided a process for the production of difluoromethane which comprises(a) fluoride to produce bis(fluoromethyl)ether is almost instantaneousand we prefer, in order to reduce the tendency for unwanted by-productsto form, that it is the bis(fluoromethyl)ether which is continuouslyseparated from the reaction mixture as soon as possible after it isformed.

Preferably therefore, the reaction between formaldehyde and hydrogenfluoride is conducted in a manner and using apparatus whereby thebis(fluoromethyl)ether is continually separated from water as they areformed. Thus for example, the reaction may be effected by "reactivedistillation" in a distillation column in which formaldehyde andhydrogen fluoride are continuously fed to the column and in which a topsstream comprising bis(fluoromethyl)ether and hydrogen fluoride, and anaqueous bottoms fraction comprising water, water/hydrogen fluorideazeotrope and unreacted formaldehyde are continually collected from thecolumn. Alternatively the reaction between formaldehyde and hydrogenfluoride may be conducted in the presence of a water-immiscible organicsolvent for the bis(fluoromethyl)ether so that as the(bis(fluoromethyl)ether is produced, the bis(fluoromethyl)ether isextracted into the solvent. These processes are described in more detailin our co-pending UK Patent Applications Nos. 9124087.9 and 92 08769.1respectively.

We have also found that bis(fluoromethyl)ether, and in particular thebis(fluoromethyl)ether compositions of the first aspect of the inventionare contacting formaldehyde with hydrogen fluoride in the vapour phaseat elevated temperature in the presence of a catalyst to produce aproduct comprising bis(fluoromethyl)ether and water (b) separating atleast a part of the water from the bis(fluoromethyl)ether and (c)feeding the bis(fluoromethyl)ether to a reaction zone whereby to producedifluoromethane.

Step (c) of these preferred embodiments of the invention, that is thethird aspect of the invention, may be effected in the liquid or vapourphase. We prefer for simplicity however, that step (c) is effected inthe vapour phase by heating the bis(fluoromethyl)ether to elevatedtemperature. Preferably therefore the bis(fluoromethyl)ether is fed to aheating zone.

The heating zone may be part of the same vessel or apparatus in whichstep (a) of the process of effected. Thus for example, the formaldehydeand hydrogen fluoride may be contacted in a distillation column aspreviously described, the bis(fluoromethyl)ether rising through thecolumn and the water falling down the column. A heating zone may beprovided towards the top of the column in which thebis(fluoromethyl)ether, separated from water, is converted todifluoromethane. Alternatively, and preferably however, in order that ascomplete separation as possible of water and bis(fluoromethyl)ether isachieved, steps (a) and (c) may be performed in separate reactionvessels.

In the second preferred embodiment of the invention, both of steps (a)and (c) may therefore employ elevated temperature and both may employ acatalyst so that in practice at least a part of thebis(fluoromethyl)ether produced in step (a) may be converted todifluoromethane (step c) without a change in reaction conditions.However, we have found that for optimum results different catalysts arepreferred in step (a) and step (c); the process then comprises operationof step (a) using a first catalyst to produce bis(fluoromethyl)ether anddifluoromethane and operation of step (c) using a second catalyst toconvert unreacted bis(fluoromethyl)ether from step (a) todifluoromethane.

In the second preferred embodiment where the formaldehyde and hydrogenfluoride are reacted in the vapour phase to produce thebis(fluoromethyl)ether, the product stream from step (a) may be passeddirectly to the second reaction zone after separating water from theproduct stream from step (a), if desired together with additionalhydrogen fluoride.

The bis(fluoromethyl) ether may be introduced into the heating zone inundiluted form although, depending upon the process employed for theproduction of the bis(fluoromethyl)ether, it may be convenient tointroduce the bis(fluoromethyl) ether vapour into the heating zone inconjunction with a diluent such as an inert carrier gas, for examplenitrogen.

The temperature to which the bis(fluoromethyl) ether is heated toproduce difluoromethane is such that the bis(fluoromethyl)ether is inthe vapour phase and the temperature will therefore be at least 80° C.,preferably at least 200° C. and more preferably at least 250° C. Thetemperature need be no higher than about 500° C., although highertemperatures, say up to about 700° C., may be used if desired.

Heating of the bis(fluoromethyl)ether may be carried out in the presenceof hydrogen fluoride vapour. The hydrogen fluoride may be used as thediluent or carrier gas with which the bis(fluoromethyl)ether isintroduced into the reaction zone or the hydrogen fluoride may beintroduced into the reaction zone separately.

The heating of the bis(fluoromethyl)ether to produce difluoromethane mayadvantageously be performed in the presence of a catalyst. Theconversion of bis(fluoromethyl)ether and selectivity to difluoromethaneare dependent in particular upon the choice of catalyst in the presenceof which the bis(fluoromethyl)ether is heated to elevated temperature.We have found that certain catalysts promote a high degree ofselectivity to difluoromethane, whilst other catalysts promote a highdegree of selectivity to trifluoromethane and other catalysts yieldmixtures of both difluoromethane and trifluoromethane.

The catalyst may be for example, a metal, for example an s-block metalsuch as calcium, a p-block metal such as aluminium, tin or antimony, anf-block metal such as lanthanum or a d-block metal such as nickel,copper, iron, manganese, cobalt and chromium or alloys thereof; a metaloxide, for example chromia or alumina, a metal fluoride, for example,aluminium, manganese or chromium fluoride, or a metal oxyfluoride, forexample an oxyfluoride of one of the aforementioned metals. The metal ispreferably a d- or p- block metal, oxide, fluoride or oxyfluoridethereof, and more preferably chromium, aluminium, or a Group VIIIametal.

We have found that difluoromethane may be produced with very highselectivity where the catalyst employed is a metal selected from thegroup consisting of nickel, aluminium, iron or chromium and inparticular where the catalyst is an alloy or mixture of at least one ofthese metals. We especially prefer to employ alloys comprising more thanone of these metals, and the alloys may also comprise other metals, forexample molybdenum. Examples of preferred alloys include Hastelloy andstainless steel; stainless steel is especially preferred.

Furthermore we prefer that these alloys are air treated prior to use,that is the alloys are heated to elevated temperature in the presence ofair, for example a temperature in the range from 300° C. to 500° C.Alternatively or additionally, this catalyst pro-treatment heating maybe carried out in the presence of hydrogen fluoride.

Further preferred catalysts are chromia and iron oxide, which althoughthey may not promote as high a degree of selectivity to difluoromethaneas the preferred alloys, are very robust catalysts. Chromia and ironoxide may also be given a pre-treatment prior to their use.

The catalyst may also comprise mixtures of metals, oxides, fluorides oroxyfluorides thereof, such as for example impregnated metal oxide oroxyfluorides, or simple mixtures. Thus, for example the catalyst maycomprise chromia impregnated with iron, nickel or other metals orcompounds thereof, for example oxides or halides thereof or the catalystmay comprise a mixture of chromia and other metal oxides, for exampleiron oxide.

Other catalysts may also be used which lead to the production ofmonofluoromethane with a high degree of selectivity, for example acatalyst comprising zinc impregnated chromia or tin fluoride.

Accordingly in a further preferred embodiment of the third aspect of theinvention there is provided a process for the production ofdifluoromethane which comprises heating bis(fluoromethyl)ether in thevapour phase at elevated temperature in the presence of a catalyst andoptionally also in the presence of hydrogen fluoride. The catalyst ispreferably at least one metal, metal oxide, metal fluoride or metaloxyfluoride.

According to a still further preferred embodiment of the invention thereis provided a process for the production of difluoromethane whichcomprises heating bis(fluoromethyl)ether in the vapour phase at elevatedtemperature in the presence of a catalyst comprising:

(i) a metal selected from the group consisting of nickel, chromium,aluminium and iron or an alloy of at least one of these metals, or

(ii) an oxide, fluoride or oxyfluoride of one of the metals or alloysdefined in (i).

The temperature to which the bis(fluoromethyl)ether is heated isdependant at least to some extent on whether the heating is effected inthe presence of a catalyst and/or one of the aforementioned metals oralloys. Where the heating is effected in the presence of a catalyst, thepreferred temperature is dependent on the particular catalyst used;generally where a catalyst or one of the aforementioned metals or alloysis present, the temperature may not be as high as when a catalyst or oneof the aforementioned metals or alloys thereof is not present.

Typically the temperature need be no higher than about 450° C. where acatalyst or one if the aforementioned metals or alloys is used in thepresence of hydrogen fluoride. Thus, for example, where the heating iseffected in the presence of stainless steel and hydrogen fluoride, thetemperature s preferably at least about 250° C. and more preferably atleast 300° C. but need be no higher than about 400° C., generally nohigher than about 350° C. However, where the fluorination catalyst ischromia in the presence of hydrogen fluoride, the temperature ispreferably from about 180° C. to about 320° C., more preferably fromabout 200° C. to about 280° C.

The process of the invention is conveniently carried out at aboutambient pressure although superatmospheric or subatmospheric pressuresmay be used if desired. Indeed superatmospheric pressures up to about 15bar at lower temperatures may be generally preferred since the yield ofand selectivity to difluoromethane may be increased under suchconditions.

After completion of the reaction, the difluoromethane may be isolatedfrom unchanged starting materials using conventional procedures, forexample distillation.

It is particularly convenient to operate the process of the invention asa continuous process wherein unchanged bis(fluoromethyl)ether and anyhydrogen fluoride present in the difluoromethane product stream arerecycled to the reaction zone.

The invention is illustrated, but not limited, the following examples.

EXAMPLE 1 Production and Isolation of BFME

114 g of anhydrous liquid hydrogen fluoride was added with cooling to 30g of paraformaldehyde prills in a 200 cc FEP (copolymer oftetrafluoroethylene and hexafluoropropylene) flask and the solution wasstirred for 12 hours at about 0° C. The solution was then added dropwiseto excess of aqueous KOH solution contained in a plastic conical flaskwhich was connected to a series of two traps, the first containingaqueous KOH solution and the second trap being empty and cooled to -78°C. for final collection of the fluoroether. After addition of theparaformaldehyde/hydrogen fluoride mixture to the aqueous KOH solution,the alkaline solution was warmed to 50° C. to drive the fluoroetherthrough to the cool trap. 6.2 g of pure ether was collected.

EXAMPLE 2 Production and Isolation of BFME

100 ml of anhydrous liquid hydrogen fluoride was added with cooling to21 g of solid trioxane in a 200 cc FEP (copolymer of tetrafluoroethyleneand hexafluoropropylene) flask and the solution was stirred for a fewminutes at room temperature. The solution was then added slowly to 700ml of water at about 50° C. in a FEP flask which was connected to aseries of traps and through which Nitrogen was continuously purged at100 ml/minute. The first trap contained anhydrous calcium chloride toremove any traces of water from the product stream and the productstream was collected in a second trap which was cooled by aDrikold/trichloroethylene bath. The product collected in the trap wasanalysed by Gas Chromatography and determined to be purebis(fluoromethyl)ether.

EXAMPLE 3 Heating BFME in Presence of Air-Treated Chromium and HF

114 g of anhydrous liquid hydrogen fluoride was added with cooling to 30g of paraformaldehyde prills in a 200 cc FEP (copolymer oftetrafluoroethylene and hexafluoropropylene). flask and the solution wasstirred for a few minutes at 10° C.

Nitrogen was bubbled through the paraformaldehyde/hydrogen fluorideliquid mixture at a flow rate of 50 cms³ /minute and the vapour was fedto an Inconel reactor charged with 200 g (70 cms³) of air-treatedchromium granules. Air-treatment was carried out by heating the chromiumgranules in an air stream (1.5 l/minute) for 16 hours at about 400° C.

The Inconel tube was heated to elevated temperature. The off gases wereanalysed by Gas Chromatography and the results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                % BFME  % Yield (moles).                                                                           Molar Ratio                                      Temp/°C.                                                                         Conversion                                                                              CH.sub.3 F                                                                             CH.sub.2 F.sub.2                                                                    CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        275       26.08     1.88     24.20 12.86                                      309       57.81     2.96     54.85 18.54                                      362       65.09     1.64     63.44 38.61                                      403       59.99     2.41     57.57 23.84                                      ______________________________________                                    

EXAMPLE 4 Heating BFME in Presence of Air-Treated Copper and HF

The procedure of example 3 was followed except that the Inconel tube waspacked with 133.5 g (170 cms³) of air-treated copper gauze. The resultsare shown in Table 2 in which the yields of CH₃ F and CH₂ F₂ are basedon the number of moles of bis(fluoromethyl)ether charged to the reactor.

                  TABLE 2                                                         ______________________________________                                               % Yield    % BFME    Molar Ratio                                       Temp/°C.                                                                        CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F.               ______________________________________                                        209      0.0    0.0       0.0     --                                          229      1.61   1.23      15.22   0.76                                        250      3.29   3.9       41.9    1.18                                        324      3.0    5.26      66.67   1.75                                        ______________________________________                                    

EXAMPLE 5 Heating BFME in Presence of Iron and HF

The procedure of example 3 was followed except that the Inconel tube waspacked with 464 g (144 cms³) of iron chips. The results are shown inTable 3, in which the yields of CH₂ F₂ and CH₃ F are based on the numberof moles of bis(fluoromethyl)ether charged to the reactor.

                  TABLE 3                                                         ______________________________________                                               % Yield    BFME       Molar Ratio                                      Temp/°C.                                                                        CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        274      1.5    0.93      2.44     0.62                                       311      3.25   4.35      7.59     1.34                                       364      6.15   16.37     23.36    2.66                                       394      7.31   24.69     34.46    3.38                                       452      10.81  55.84     76.10    5.16                                       ______________________________________                                    

EXAMPLE 6 Heating BFME in Presence of Air-Treated Nickel and HF

The procedure of example 3 was followed except that the Inconel reactorwas packed with 402 g (80 cms³) of air-treated nickel balls. The resultsare shown in Table 4, in which the yields of CH₂ F₂ and CH₃ F are basedon the number of moles of bis(fluoromethyl)ether charged to the reactor.

                  TABLE 4                                                         ______________________________________                                                % Yield    % BFME    Molar Ratio                                      Temp/°C.                                                                         CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        305       2.62   2.39      5.01    0.91                                       334       3.73   9.56      13.29   2.57                                       366       5.83   23.41     29.24   4.01                                       399       6.51   41.47     47.98   6.37                                       463       11.92  55.13     68.73   4.62                                       ______________________________________                                    

EXAMPLE 7 Heating BFME in Presence of Air-Treated Hastelloy C and HF

The procedure of example 3 was followed except that the Inconel reactorwas packed with 83.6 g (150 cms³) of air-treated Hastelloy C foilpieces. The results are shown in Table 5, in which the yields of CH₂ F₂and CH₃ F are based on the number of moles of bis(fluoromethyl)ethercharged to the reactor.

                  TABLE 5                                                         ______________________________________                                                % Yield    % BFME    Molar Ratio                                      Temp/°C.                                                                         CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        209       0.82   3.49      4.31    4.24                                       242       1.25   12.75     13.99   10.23                                      300       1.92   40.82     42.74   21.29                                      343       2.80   59.89     62.70   21.36                                      387       3.70   78.74     82.45   21.28                                      428       5.32   85.23     90.55   16.04                                      466       7.41   90.56     97.98   12.22                                      ______________________________________                                    

EXAMPLE 8 Heating BFME in Presence of Hastelloy C and HF

The procedure of example 7 was followed except that the Inconel reactorwas packed with 83.6 g (150 cms³) of Hastelloy C foil pieces, which hadnot been air-treated. The results are shown in Table 6, in which theyields of CH₂ F₂ and CH₃ F are based on the number of moles ofbis(fluoromethyl)ether charged to the reactor.

                  TABLE 6                                                         ______________________________________                                                % Yield    % BFME    Molar Ratio                                      Temp/°C.                                                                         CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        257       0.42   1.87      2.28    4.5                                        299       0.92   8.03      8.95    8.74                                       330       1.46   16.64     18.10   11.43                                      356       1.94   31.01     32.95   16.00                                      384       2.59   49.53     52.12   19.15                                      418       3.32   60.02     63.35   18.05                                      472       4.67   59.91     64.58   12.83                                      ______________________________________                                    

EXAMPLE 9 Heating BFME in Presence of Air-Treated Stainless Steel Grade304 Mesh and HF

The procedure of example 3 was followed except that the Inconel reactorwas packed with 82.8 g (200 cms³) of air-treated stainless steel grade304 mesh. The results are shown in Table 7, in which the yields of CH₂F₂ and CH₃ F are based on the number of moles of bis(fluoromethyl)ethercharged to the reactor.

                  TABLE 7                                                         ______________________________________                                               % Yield     % BFME    Molar Ratio                                      Temp/°C.                                                                        CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        229      6.41    85.85     92.26   13.40                                      258      7.36    86.72     94.08   11.78                                      296      10.16   86.34     96.51   8.49                                       320      10.68   86.30     96.98   8.76                                       364      11.97   85.90     97.87   7.18                                       400      10.692  85.68     99.13   8.01                                       ______________________________________                                    

EXAMPLE 10 Heating BFME in Presence of Stainless Steel Grade 304 Meshand HF

The procedure of example 9 was followed except that the Inconel reactorwas packed with 82.8 g (200 cms³) of stainless steel grade 304 mesh,which had not been air-treated. The results are shown in Table 8, inwhich the yields of CH₂ F₂ and CH₃ F are based on the number of moles ofbis(fluoromethyl)ether charged to the reactor.

                  TABLE 8                                                         ______________________________________                                                % Yield    % BFME    Molar Ratio                                      Temp/°C.                                                                         CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        295       0.28   0.30      0.58    1.05                                       336       3.94   6.91      10.85   1.75                                       369       19.34  58.61     83.15   3.03                                       395       10.05  51.51     74.85   5.12                                       ______________________________________                                    

EXAMPLE 11 Heating BFME in Presence of Air-Treated Stainless Steel Grade316 Rings and HF

The procedure of example 3 was followed except that the Inconel reactorwas packed with 133.5 g (200 cms³) of air-treated stainless steel grade316 rings, and the example was conducted isothermally and thecomposition of the off-gas monitored at regular intervals. The resultsare shown in Table 9, in which the yields of CH₂ F₂ and CH₃ F are basedon the number of moles of bis(fluoromethyl)ether charged to the reactor.

                  TABLE 9                                                         ______________________________________                                                % Yield    % BFME    Molar Ratio                                      Temp/°C.                                                                         CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion                                                                            CH.sub.2 F.sub.2 /CFH.sub.3                ______________________________________                                        316       6.41   92.72     94.28   14.46                                      316       7.36   93.63     95.38   12.72                                      316       10.16  95.50     97.86   9.4                                        316       10.68  90.00     94.51   8.43                                       316       11.97  90.62     96.95   7.57                                       ______________________________________                                    

EXAMPLE 12 Heating BFME in Presence of Stainless Steel Grade 316 Ringsand HF

The procedure of example 11 was followed except that the Inconel reactorwas packed with 133.5 g (200 cms³) of stainless steel grade 316 mesh,which had not been air-treated. The results are shown in Table 10, inwhich the yields of CH₂ F₂ and CH₃ F are based on the number of moles ofbis(fluoromethyl)ether charged to the reactor.

                  TABLE 10                                                        ______________________________________                                                % Yield       % BFME    Molar Ratio                                   Temp/°C.                                                                         CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                       Conversion                                                                            CH.sub.2 F.sub.2 /CH.sub.3 F                ______________________________________                                        188       0.00   0.00     0.00    --                                          231       0.31   1.71     2.03    5.5                                         266       0.66   6.97     7.63    10.6                                        295       0.96   12.94    13.91   13.5                                        325       1.53   18.57    20.10   12.1                                        339       3.17   35.06    38.24   11.1                                        357       5.23   67.06    72.77   12.8                                        367       6.75   91.45    99.22   13.5                                        ______________________________________                                    

EXAMPLE 13 Heating BFME in Presence of Aluminium Fluoride

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 50 cms³/minute. The vapour was fed to an Inconel tube (length 18 inches anddiameter 1 inch) packed with 200 cms³ of aluminium fluoride pellets andthe tube was heated from room temperature to an elevated temperatureover a period of 5 hours.

Three runs were carried out at various temperatures. The reactor off gaswas followed as a function of temperature and the results are shown inTable 11.

                  TABLE 11                                                        ______________________________________                                        % Yield (moles)          MOLAR RATIO                                          TEMP/°C.                                                                      CH.sub.4                                                                             CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                    BFME  Others                                                                              CH.sub.2 F.sub.2 /CH.sub.3             ______________________________________                                                                               F                                      145    --     1.15   1.15  91.7  6.0   1.0                                    340    --     3.69   3.29  48.9  44.1  0.89                                   405    3.39   21.5   19.8  35.0  20.1  0.92                                   ______________________________________                                    

EXAMPLE 14 Heating BFME in Presence of Aluminium Fluoride and HF

The procedure of example 3 was followed except that the Inconel tube waspacked with 200 cms³ of aluminium fluoride pellets. The results areshown in Table 12, in which the yields of CH₂ F₂ and CH₃ F are based onthe number of moles of bis(fluoromethyl)ether charged to the reactor.

                  TABLE 12                                                        ______________________________________                                        % Yield (moles)          MOLAR RATIO                                          TEMP/°C.                                                                      CH.sub.4                                                                             CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                    BFME  Others                                                                              CH.sub.2 F.sub.2 /CH.sub.3             ______________________________________                                                                               F                                      155    --     3.06   0.08  81.6  15.1  0.03                                   257    0.05   37.9   20.12 20.2  21.6  0.53                                   343    1.5    10.5   16.2  10.4  73.5  1.54                                   398    9.2    0.4    26.2  3.6   61.0  65.5                                   ______________________________________                                    

EXAMPLE 15 Heating BFME in Presence of Zinc Impregnated Chromia Catalystand HF

The procedure of example 3 was followed except that the Inconel tube waspacked with 135 g (200 cms³) of zinc impregnated chromia pellets.

The zinc impregnated chromia pellets were prepared by immersing chromiapellets in aqueous zinc chloride so that all surfaces of the chromiawere wetted and drying the pellets in air by direct heating.

The results are shown in Table 13, in which the yields of CH₂ F₂ and CH₃F are based on the number of moles of bis(fluoromethyl)ether charged tothe reactor.

                  TABLE 13                                                        ______________________________________                                        % Yield               BFME       Molar Ratio                                  Temp/°C.                                                                       CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        172     82.42   1.39      83.81    0.02                                       192     93.96   2.14      96.11    0.02                                       218     97.58   2.09      99.67    0.02                                       267     100.00  0.00      100.0    0.00                                       193     100.00  0.00      100.0    0.00                                       160     93.85   2.85      97.65    0.03                                       ______________________________________                                    

EXAMPLE 16 Heating BFME in Presence of Air-Treated Chromia and HF

The procedure of example 3 was followed except that the Inconel tube waspacked with 200 cms³ of air-treated chromia pellets. The results areshown in Table 14, in which the yields of CH₂ F₂ and CH₃ F are based onthe number of moles of bis(fluoromethyl)ether charged to the reactor.

                  TABLE 14                                                        ______________________________________                                        % Yield               BFME       Molar Ratio                                  Temp/°C.                                                                       CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        174     35.5    30.9      66.4    0.87                                        216     46.6    43.3      89.9    0.98                                        225     44.2    48.4      92.6    1.10                                        230     43.6    48.35     92.0    1.11                                        ______________________________________                                    

EXAMPLE 17 Heating BFME in the Presence of HF-Treated Chromia

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to an Inconel tube (length 12 inches anddiameter 1 inch) packed with 120 g of chromia pellets which had beenpre-treated by heating the pellets to 350° C. for 4 hours in a stream ofhydrogen fluoride having a flow rate of 150 ml/minute. The tube washeated from room temperature to elevated temperature and the compositionof the reactor off gas was followed (Gas Chromatography) as a functionof temperature and the results are shown in Table 15.

                  TABLE 15                                                        ______________________________________                                        % Yield               BFME       Molar Ratio                                  Temp/°C.                                                                       CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        185     29.11   43.79     74.38    1.5                                        224     32.34   62.54     95.71    1.93                                       246     35.40   63.77     99.97    1.8                                        256     35.22   62.21     100.0    1.77                                       292     35.66   57.45     98.09    1.61                                       320     35.88   54.57     97.62    1.52                                       ______________________________________                                    

EXAMPLE 18 Heating BFME in the Presence of Iron (III) Doped Chromia

100 g of chromia pellets were added to an aqueous solution of iron (III)nitrate and the water was then removed by direct heating to give a 2.6%Iron (III) impregnated chromia catalyst. 100 g of the catalyst wascharged to an Inconel reactor (length 12 inches and diameter 1 inch) andheated in nitrogen at 300° C. for 28 hours and then pre-fluorinated byheating in hydrogen fluoride at 350° C. for 12 hours. Finally thecatalyst was heated in nitrogen at 250° C. for 15 hours.

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to the Inconel reactor. The tube washeated from room temperature to elevated temperature and the compositionof the reactor off gas was followed (Gas Chromatography) as a functionof temperature and the results are shown in Table 16.

                  TABLE 16                                                        ______________________________________                                        % Yield               BFME       Molar Ratio                                  Temp/°C.                                                                       CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        232     23.32   70.72     94.27    3.03                                       250     22.59   73.92     99.87    3.27                                       265     20.89   76.36     98.93    3.66                                       272     19.15   77.24     99.63    4.03                                       288     17.65   77.10     99.79    4.37                                       300     19.34   77.80     99.45    4.02                                       ______________________________________                                    

EXAMPLE 19 Heating BFME in the Presence of Iron (II) Doped Chromia

85 g of the Iron (III) doped chromia catalyst prepared as described inexample 18 were charged to an Inconel reactor as described in Example 18and heated in hydrogen at 375° C. to reduce iron (III) to iron. Thecatalyst was then pre-fluorinated by heating in hydrogen fluoride at350° C. for 12 hours to oxidise the iron to iron (II).

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to the Inconel reactor. The tube washeated from room temperature to elevated temperature and the compositionof the reactor off gas was followed (Gas Chromatography) as a functionof temperature and the results are shown in Table 17.

                  TABLE 17                                                        ______________________________________                                        % Yield               BFME       Molar Ratio                                  Temp/°C.                                                                       CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        235     16.09   61.86     77.95    3.84                                       256     10.51   68.70     79.22    6.54                                       270     9.23    66.58     75.81    7.21                                       ______________________________________                                    

EXAMPLE 20 Heating BFME in the Presence of Nickel Doped Chromia

100 g of chromia pellets were added to a saturated aqueous solution ofnickel nitrate and the water was then removed by direct heating to 150°C., to give a 2.7% nickel impregnated chromia catalyst. 100 g of thecatalyst was charged to an Inconel reactor (length 12 inches anddiameter 1 inch) and heated in nitrogen at 300° C. for 28 hours and thenpre-fluorinated by heating in hydrogen fluoride at 350° C. for 4 hours.Finally the catalyst was heated in nitrogen at 250° C. for 15 hours.

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to the Inconel reactor. The tube washeated from room temperature to elevated temperature and the compositionof the reactor off gas was followed (Gas Chromatography) as a functionof temperature and the results are shown in Table 18.

                  TABLE 18                                                        ______________________________________                                        % Yield               BFME       Molar Ratio                                  Temp/°C.                                                                       CH.sub.3 F                                                                            CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        223     36.78   60.35     97.14    1.64                                       234     28.25   69.10     97.35    2.45                                       241     21.60   77.56     99.16    3.6                                        251     23.42   73.27     97.82    3.13                                       265     26.48   71.64     98.12    2.7                                        279     24.45   72.35     99.53    3.0                                        ______________________________________                                    

EXAMPLE 21 Heating BFME in the Presence of Mixed Iron Oxide/Chromia

112.7 g of a catalyst comprising 9:1 by weight iron (III) oxide andchromia was charged to an Inconel reactor (length 12 inches and diameter1 inch) and heated in hydrogen fluoride at 300° C. for 12 hours. Thecatalyst was then heated in nitrogen at 230° C. for 15 hours.

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to the Inconel reactor. The tube washeated from room temperature to elevated temperature and the compositionof the reactor off gas was followed (Gas Chromatography) as a functionof temperature and the results are shown in Table 19.

                  TABLE 19                                                        ______________________________________                                                 % Yield      BFME       Molar Ratio                                  Temp/°C.                                                                        CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        223      23.34  73.52     99.15    3.15                                       235      19.33  68.41     87.75    3.54                                       ______________________________________                                    

EXAMPLE 22 Heating BFME in the Presence of Pre-Fluorinated AluminiumFluoride

103.9 g of aluminium fluoride was charged to an Inconel reactor (length12 inches and diameter 1 inch), heated in nitrogen at 300° C. for 4hours and then heated in hydrogen fluoride at 300° C. for 12 hour's. Thecatalyst was then heated in nitrogen at 240° C. for 16 hours.

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to the Inconel reactor. The tube washeated from room temperature to elevated temperature and the compositionof the reactor off gas was followed (Gas Chromatography) as a functionof temperature and the results are shown in Table 20.

                  TABLE 20                                                        ______________________________________                                                 % Yield      BFME       Molar Ratio                                  Temp/°C.                                                                        CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        235      30.46  68.5      98.96    2.25                                       ______________________________________                                    

EXAMPLE 23 Heating BFME in the Presence of Chromia and Hydrogen Fluorideat Elevated Pressure

Bis(fluoromethyl)ether was vaporised by bubbling nitrogen through liquidbis(fluoromethyl)ether at room temperature at a flow rate of 75mls/minute. The vapour was fed to an Inconel tube (diameter 0.37 inch)packed with 15 mls of chromia pellets. Hydrogen fluoride was also fed tothe reactor at a flow rate of 0.038 g/minute by passing 44 mls/minute ofnitrogen through a bomb containing liquid hydrogen fluoride. The reactorwas pressurised to 15 barg.

The tube was heated from room temperature to elevated temperature andthe composition of the reactor off gas was followed (Gas Chromatography)as a function of temperature and the results are shown in Table 21.

                  TABLE 21                                                        ______________________________________                                                 % Yield      BFME       Molar Ratio                                  Temp/°C.                                                                        CH.sub.3 F                                                                           CH.sub.2 F.sub.2                                                                        Conversion/%                                                                           CH.sub.2 F.sub.2 /CH.sub.3 F               ______________________________________                                        240      39.0   29.6      95.0     0.76                                       ______________________________________                                    

EXAMPLES 24 TO 29

In the following examples, 1 ml of the catalyst in a finely divided formwas charged to a 0.5 mm internal diameter stainless steel reactor tubeand bis(fluoromethyl)ether was pumped through a vaporiser to give abis(fluoromethyl)ether vapour feed with a flow rate of 5 ml/minute. Thisstream was mixed with 10 ml/minute nitrogen and the mixed stream passedover the catalyst at the temperature given in Table 22. The reactor offgas was analysed by gas chromatography and the results are shown inTable 22.

                  TABLE 22                                                        ______________________________________                                                             TEMP       % Yield                                       EXAMPLE    CATALYST  °C. CH.sub.2 F.sub.2                                                                    CH.sub.3 F                              ______________________________________                                        24         HgF.sub.2 400        40    N/D                                     25         LaF.sub.3 350        84    N/D                                     26         SnF.sub.2 450        N/D   4                                       27         MnF.sub.3 240        23    N/D                                     28         CrF.sub.3 200        50    25                                      29         FeF.sub.3 340        11    N/D                                     ______________________________________                                    

EXAMPLE 30

1 g of CaF₂ was charged to an Inconel reactor heated at 240° C. Hydrogenfluoride was passed over the catalyst for 15 minutes at 4.5 ml/minuteafter which a bis(fluoromethyl)ether feed (1.5 ml/minute) was alsopassed over the catalyst. The temperature was increased to 350° C. andthe reactor off-gases were analysed by gas chromatography. Analystsshowed that the gases comprised 90% bis(fluoromethyl)ether, 9.5% CH₂ F₂,and 0.5% CH₃ F.

EXAMPLE 31

Formaldehyde monomer, generated by heating paraformaldehyde was fed at80 cm³ /minute on a stream of nitrogen (400 cms³ /minute) to an Inconelreactor tube charged with a catalyst comprising CsF supported oncharcoal, whilst co-feeding hydrogen fluoride at 1000 cm³ /minute. Thereactor tube was heated to 300° C. The reactor off-gases were scrubbedto remove hydrogen fluoride and analysed by gas chromatography. Thereactor off-gases comprised 48.5% bis(fluoromethyl)ether.

We claim:
 1. A composition comprising bis(fluoromethyl)ether and water wherein the molar ratio of bis(fluoromethyl)ether to water in the composition is at least 10:1.
 2. A composition according to claim 1, said composition consisting essentially of the reaction product of formaldehyde and liquid hydrogen fluoride and being substantially free from water. 